meiosis eq: how is meiosis different from mitosis?
TRANSCRIPT
MEIOSISEQ: How is meiosis different
from mitosis?
Chromosome
DNA
Gene
DIPLOID CELL= a cell with 2 of each kind of chromosome
_______________Chromosomes
Mom 1
Dad 1
“Homologous”
?
“Complete Set”__ Mom__ Dad
Dad 1
Mom 1
“__n”
“autosomes”
“sex chromosomes”
2
23
23
__Total46
Haploid Cell
= a cell with 1 of each kind of chromosome
“n”_____TotalChromosomes
23
or
“Gamete”(male/female)
Haploid + Haploid = ?n n 2n
“Zygote”
___ ___ ___
________
2323
23
23
23
The first cell is called a
WHY NOT ONLY MITOSIS?
• Mitosis produces an exact replica
Each parent would give a complete set of chromosomes(46)
Baby wouldn’t be Human
MEIOSIS= Sexual Cell Division Halving the chromosome #
1 Body Cell ?
Replicate DNA once and Divide?Twice
4 Eggs or 4 Sperm
1 Diploid (2n) 4 Haploid (n)
46 pairs
46 46
23 23 23 23
46
PHASES OF MEIOSIS
• Meiosis I
Interphase
PMAT I
• Meiosis II
PMAT II
FirstInterphase
Meiosis I
46
46 pairs
46 46
Meiosis II
= 4 Gametes
46 46
23 23 23 23
1 Diploid (2n) ?
46
92
46 46
23 23 23 23
Interphase
PMAT I
PMAT II
?
?
4 Haploid (n)
• Meiosis I occurs in four phases: prophase, metaphase, anaphase, and telophase.
Interphase?Chromosomes replicate Sister Chromatids
Centrosomes
• Prophase I =– the chromosomes condense and homologous chromosomes pair
up to form tetrads.
– At several sites the chromatids are crossed (chiasmata) and segments of the chromosomes are traded
(“crossing over”).
• Metaphase I = • the tetrads are all arranged at the metaphase plate.
• Anaphase I = the homologous chromosomes separate and are pulled toward opposite poles.
• Telophase I = – movement of homologous chromosomes continues
until there is a set at each pole.– Each chromosome consists of linked sister chromatids.
• Cytokinesis =usually occurs simultaneously.
• “NO further replication of chromosomes”
• Meiosis II is very similar to mitosis.Prophase II =
• Metaphase II =
• Anaphase II =
• Telophase II =
• Cytokinesis =
• End ?
four haploid daughter cells.
#? 46
#?#?
#?
46
23 each
92#?
Animation
P I M I
A I T I--------
4n
2n 2n
Interphase:ChromosomeDuplicate
P II M II
A II T II
- - - - - - - - - - - - - - - - -
-------
--------
-------
-------
- - - - - - - - - - - - - - - - -
n n
n n
Interphase:NoDuplication
Sperm (n) to Egg (n) = Zygote (2n)
• Fertilization restores the diploid condition by combining two haploid sets of chromosomes.
GENETIC VARIABILITYMeiosis “shuffles” genetic information
3 ways of “shuffling”
Dad
Mom
“Independent Assortment”
----
----
Human Gamete = 23n
– Egg: 223 = 8.4 million
– Sperm: 223 = 8.4 million
Egg + Sperm = 70 trillion possibilities
“Recombinant Chromosomes”
“Crossing Over”
“Random Fertilization”
200 – 500 million per ejaculation 1 egg
One “winner”
GENETIC VARIABILITY
Evolutionary adaptation?
THE CELL CYCLE, MITOSIS, and MEIOSIS
The Cell Cycle
2 Main PhasesTime Spent in eachWhat happens in all phasesStages of InterphaseChromosomes DNA Replication
Mitosis
Phases of MitosisCytokinesisChromosomes vs. ChromatidsChromosome NumberDiploidSomaticCancer
Meiosis
HaploidGametesPhases of MeiosisTetrads Crossing OverGenetic Variability